The bedrock of the island of Viðey can be grouped into two different formations. Firstly is an interglacial lava flow on the western part of the island (Vesturey) which is from one of the interglacial periods of the Ice Age. Secondly are rocks belonging to the Viðey central volcano. The volcano was active about 2 million years ago. The rocks belonging to the volcano are mainly of two types. Hyaloclastites and small intrusive bodies.
Haukur Jóhannesson, 2010